A novel type of transposon generated by insertion element IS102 present in a pSC101 derivative

We describe a novel type of transposon in the tetracycline resistance plasmid pYM103, a derivative of pSC101 carrying a single copy of an insertion element IS102. The new transposons we found were identified as DNA segments, approximately 6 kb (Tn1021) and 10 kb (Tn1022) in length, able to mediate the cointegration of pYM103 with plasmid Col E1. The resulting cointegrate contains either of these pYM103 segments duplicated in a direct orientation at the junctions of the parent plasmids. A direct duplication of a 9 bp sequence at the target site in Col E1 is found at the junctions for cointegration. Both transposons have IS102 at one end and also contain different lengths of the pYM103 DNA adjacent to IS102, including the tetracycline resistance gene. Each transposon contains terminal inverted repeats of a short nucleotide sequence. These results and the fact that IS102 can itself mediate plasmid cointegration, giving rise to a duplication of a 9 bp target sequence, indicate that IS102 is responsible for generation of Tn1021 and Tn1022. They are quite different from the common IS-associated transposons, which are always flanked by two copies of an IS element, and may be similar to transposons such as those of the Tn3 family and phage Mu.

Factors determining frequency of plasmid cointegration mediated by insertion sequence IS1

We demonstrate that mutants with deletions at either end of the insertion sequence IS1 lose the ability to mediate cointegration of two plasmids, whereas mutants with deletions or an insertion within IS1 can mediate cointegration at a reduced frequency. These results, together with the nucleotide sequence analysis of the IS1 mutants, indicate that the two ends of IS1 (insL and insR) and two genes (insA and insB) that are encoded by IS1 are required for cointegration. Using a plasmid carrying two copies of IS1, we found that the individual IS1s mediate cointegration at different characteristic frequencies, and that each of two parts of plasmid DNA segments flanked by the two IS1s is a transposon, mediating plasmid cointegration at a unique frequency. When one IS1 was replaced with a mutant IS1, the remaining wild-type IS1 complemented the cointegration ability of the mutant IS1 as well as a resulting mutant transposon that was then flanked by a wild-type IS1 and a mutant IS1. The efficiency of this complementation reflected the characteristic ability of an individual IS1 present on the plasmid to promote cointegration. The results suggest that the IS1-encoded proteins are produced in different amounts, depending on the location of IS1 in the plasmid, and that these amounts determine the efficiency of complementation of the cointegration ability of a mutant IS1 as well as a mutant transposon. However, the location of an individual IS1 itself can also determine the frequency of cointegration in the presence of a given amount of the IS1 proteins. On the basis of the observation that the cointegration ability of a mutant IS1 is less efficiently complemented than is the ability of a mutant transposon, we also suggest that the IS1-encoded proteins can function in trans, but act preferentially on the IS1 or transposon sequence from which they are produced in promoting cointegration.

Local therapy of carcinoma of the uterine cervix: part I

One-hundred-fifteen patients with cervical cancer were treated by placing bleomycin, carbazilquinone (Carboquone), and 5-fluorouracil suppositories in contact with cancer lesions located in the vaginal portion of the uterus or by inserting them into the cervical canal, twice a week, one to 14 times. The cancer lesions disappeared form 17 to 33 patients with Stage 0 lesions and 9 of 42 with Stage IA lesions. The remaining lesions were principally found in the deep portion of the cervical glands and tended to decrease the more often the suppositories were applied. This led to the presumption that if this local therapy had been carried on longer it would have eradicated even the remaining lesions from the patients with Stage 0 and IA lesions. The optimal per administration dose of bleomycin appeared to be 30 mg. The use of Witepsol (Dynamit Nobel Aktiengesellschaft, F.R.G.) suppository base was accompanied by frequent adverse reactions to it, which hindered the local therapy from being repeated over long periods of time. An equal amount mixture of hydroxypropyl cellulose and carbomer (Carbopol 934) as the suppository base was accompanied by relatively less adverse reactions, which permitted the prolonged local therapy with the suppositories. A trace of bleomycin was also found in the ovaries, but it did not cause microscopically evident histologic changes, nor did it affect the menstrual cycle. If early cancer can be treated completely by local therapy, it will be useful for the younger patient with early cervical cancer.

Characterization of nascent DNA fragments produced by excision of uracil residues in DNA

Nascent short DNA chains could result from repair of incorporated uracil residues or be intermediates in discontinuous replication. We have characterized short DNA chains having apyrimidinic/apurinic-sites at 5' ends, the expected intermediates of repair, to distinguish them from RNA-linked replication intermediates. We have synthesized model substrates for the repair products; d(pRib[32P]poly(T)) and d(Rib[32P]poly(T)). Alkaline hydrolysis of both substrates has produced [5'-32P]poly(dT). Nascent short DNA was prepared from an Escherichia coli sof (dut) mutant, in this strain fragments from excision repair of uracil residues accumulate. The products of alkaline treatment are hardly digested by spleen exonuclease which selectively degrades 5'-hydroxyl-terminated DNA. These two results show that alkaline hydrolysis of the uracil repair fragments produces 5'-phosphoryl-terminated DNA, whereas it is known that 5'-hydroxyl-terminated DNA is generated from RNA-linked DNA molecules. The two types of nascent fragments thus can be distinguished by the 5'-terminal structure produced by an alkaline hydrolysis.